A wide variety of medical procedures, including standard biopsies, bone biopsies, mammogram-directed biopsies, stereotaxis, lesion drainage, and discolysis, require extremely accurate placement and insertion of medical instruments (such as needles, localization wires or other biopsy tools). Precision placement and insertion of the instrument throughout the procedure is critical to its success and serves to decrease procedure time, which in turn decreases patient discomfort, and potential for complications.
An initial step in many medical procedures such as biopsies is a CT scan (computerized tomography). This procedure provides the physician with a cross-sectional image of a patient through a "cut" or "scan" plane which shows internal organs, tissues, bony structures and abnormalities. Through the use of CT scans, physicians are able to accurately locate abnormal tissues, tumors, lesions, etc., and then can select the optimum insertion point for the appropriate instrument, whether it is a biopsy needle, drainage catheter or other instrumentation, to extract or otherwise treat the abnormality.
Using available CT scanner technology, both the insertion depth and angle required for a biopsy needle can be ascertained with a very high degree of accuracy. The limitation in actual practice, however, is the accuracy of inserting the biopsy needle by the physician, particularly with respect to insertion angle and plane. Utilizing a trial and error technique, some practitioners initially position the needle or catheter by estimating the desired angle and then slowly advance the needle into the patient's body, taking repeated CT scans during the procedure to determine the actual depth and position of the needle and altering its trajectory as required. This trial and error technique has significant disadvantages, including the relatively long time-frame required, the attendant discomfort to the patient, and increased risk due to repeated punctures and/or poor initial positioning of the instrument. Additionally, the multiple CT scans tie up available CT scan time, which is highly sought after, and increases the patient's exposure to radiation.
Certain advancements have been made which offer improvements over the trial and error method for performing CT-based biopsies and other procedures. For example, U.S. Pat. Nos. 4,638,799 and 4,706,665 relate to mechanical guide apparatus for discolysis and stereotactic procedures, respectively. U.S. Pat. No. 4,723,544 discloses another mechanical guide device for discolysis procedures. U.S. Pat. Nos. 4,733,661, 4,930,525 and 5,102,391 relate to guidance devices for CT-guided drainage and biopsy procedures. U.S. Pat. No. 5,100,411 relates to another stereotactic guidance device. Additionally, the article "CT-Guided Core Biopsy Using A New Guidance Device," A. Magnusson and D. Akerfeldt, Acta Radiol 1991; 32: pp. 83-85, discusses a mechanical biopsy guidance device. Generally, the devices disclosed in the above-referenced patents and publication are rigidly fixed to the CT scanner. Such devices have several drawbacks, however, including the requirement of precise attachment and alignment relative to the CT scanner. Furthermore, the device may obstruct the field of operation of the physician, and requires the biopsy procedure to be performed at the location of the CT scanner. Other disclosed devices are separate from the CT scanner, but attach to the ceiling, walls or to the floor. Some devices physically hold the needle or biopsy tool and therefore require sterilization before each use. In addition, some of the above devices provide no means for ensuring accurate placement of the biopsy tool in the scan plane (i.e., transverse to the patient) as they relate only to measuring and maintaining the needle insertion angle relative to a longitudinal vertical plane through the patient.
Yet another system which has been developed is described in "A Light-Guidance System To Be Used For CT-Guided Biopsy," P. Frederick et al., Radiology, Vol. 154, pp. 535-536. The system disclosed in this article is based on the principle of two intersecting planes represented by thin sheets of light. The intersection of the planes defines a line which can be positioned to define the correct insertion angle of the biopsy device. In use of this system, the biopsy instrument is held so that during its insertion it casts shadows in both beams of light, thus theoretically assuring that the instrument is following the preselected path of the line defined by the intersection of the two planes. This system has several disadvantages, however, including the requirement of two separate light sources which must be kept in alignment for the system to work properly. This beam-alignment must be made with an extremely high degree of accuracy since the light sources are positioned a considerable distance from the patient. This system presents the additional difficulty of requiring the physician to maintain the biopsy tool in line with the two planes of light simultaneously to create a shadow in each.
Thus, there is a need for a highly accurate, portable guidance or alignment apparatus which does not require sterilization or attachment to or modification of a CT scanner. Such an apparatus should be capable of use at a site remote from the CT scanner, thus freeing up the scanner for use on other patients, while insuring highly accurate positioning and insertion of a needle or other biopsy tool into a patient.